In a blood extracorporeal circulation therapy such as hemodialysis and apheresis in which patient's blood is once taken out of a body and returned into the body again, it is necessary to frequently insert a needle into a blood vessel. If a puncture into a blood vessel is frequently performed, an aneurysm may be formed or vasoconstriction may occur. A blood access (blood vessel reaching method) has been proposed that uses an indwelling type apparatus capable of reducing the number of punctures into a blood vessel. In a blood access disclosed in Patent Document 1, a blood chamber connected through a cannula to a blood vessel includes a diaphragm, and a needle is inserted into the diaphragm to perform introduction of blood, etc., into the blood vessel, leading-out of blood from the blood vessel, etc., through this needle. Since the puncture is repeatedly made into the diaphragm, the damage to the blood vessel is alleviated.